JPH03133632A - Heat transfer pipe for u-shape type heat exchanger and manufacture therefor - Google Patents

Abstract

PURPOSE:To avoid corrosion even when the title heat exchanger is utilized in the area severe in the corrosive environment by forming an organic resin film having the specified film thickness on the inner face of a pipe in the region except the specified region from both ends of the pipe. CONSTITUTION:A protective film 4 made of organic resin or iorganic substance incorporating iron hydroxide, etc., as a main component is formed in the film forming part 2 on the inner face of the stock pipe 3 of a heat transfer pipe which is bent and worked to a U-shape type. Both ends parts of the stock pipe 3 are made to a film- unformed part 1. The length in the axial direction of this film-unformed part 1 is at least 50 mm. The stock pipe 3 of the heat transfer pipe made of copper or copper alloy is exposed in this film-unformed part 1. Further film thickness of the protective film 4 in a film forming part 2 is regulated to 1 - 100mum. Anticorrosive effect is high because the protective film is formed on the inner face of the pipe having a shape bent to the U-shape. Further the film 4 is not formed in the region over at least 50 mm from the end parts of the pipe. Accordingly the film substance is prevented from being stuck to a pipe expander in the pipe expanding work when the heat transfer pipe is built-up to a heat exchanger.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a heat transfer tube for a heat exchanger in which cooling water such as seawater, river seawater or fresh water flows through the tube, and a method for manufacturing the same.
The present invention relates to a heat exchanger tube for a U-shaped heat exchanger, which is curved into a U-shape and has a corrosion-resistant protective coating formed on its inner surface to prevent corrosion by cooling water, and a method for manufacturing the same.

[Prior Art] As a heat exchanger tube for a heat exchanger in which seawater, river/seawater, or fresh water is passed through the inner surface of the tube as cooling water, a tube material made of copper or a prepared alloy has conventionally been used. In this case, in order to prevent corrosion caused by cooling water, a protective film containing, for example, iron hydroxide as a main component is often formed on the inner surface of the tube. Generally, this protective film containing iron hydroxide or the like as a main component is formed by injecting ferrous ions or the like into cooling water flowing through a heat exchanger. However, this method requires a certain period of time after the start of water flow until a protective film is formed.
The disadvantage is that the film cannot be formed on the inner surface of the heat exchanger tube in time, and a sufficient anticorrosion effect cannot be obtained.

Therefore, a method has been adopted in which a protective film such as an anticorrosive coating is formed in advance before the heat exchanger is put into use. In this type of heat exchanger tube for a heat exchanger, the protective coating needs to be formed thin and uniformly in order to prevent a decrease in heat transfer performance due to the coating. For this reason, such a protective film is generally formed by passing a spray nozzle onto the inner surface of the tube and spraying a film-forming substance from the spray nozzle.

[Problems to be Solved by the Invention] Conventionally, however, heat exchanger tubes with inner protective coatings have been limited to straight tubes, and in the case of heat exchangers that use bent tubes curved in a U-shape, However, there is a problem that this technology has not been put into practical use.

That is, when forming a protective film on the inner surface of a heat exchanger tube for a heat exchanger, as described above, this is done by passing the spray nozzle into the tube while spraying the film-forming substance from the spray nozzle.

However, in the case of a U-shaped curved tube, it is difficult to form a protective coating on the inner surface of the tube in advance because the spray nozzle cannot pass through the entire length of the tube.

In addition, it is possible to manufacture a U-shaped heat exchanger tube with an inner surface protective coating by forming a coating on the inner surface of the tube in a straight tube state and then bending the tube into a U-shape. In this case, the protective coating needs to have a large enough ductility to follow the deformation of the pipe due to normal bending, and in fact, such a resin coating is available. However, in the case of copper or copper alloy heat exchanger tubes, if they are used as a heat exchanger without removing the residual stress generated by bending, there is a risk that stress corrosion cracking or the like may occur. Therefore, in this case, after the straight pipe is bent into a U-shape, it is necessary to perform an annealing treatment to remove stress. Therefore, the coating formed on the inner surface of the tube needs to be able to withstand the high temperatures during annealing.

However, common organic resins cannot withstand the high temperatures during this annealing treatment.

Note that some inorganic films can withstand high temperatures during annealing treatment. However, in the case of an inorganic film, it cannot be bent into a U-shape because it has no ductility.

For these reasons, it is not possible to form a protective film on U-shaped heat exchanger tubes in advance, and ferrous ions are injected into the cooling water after the heat exchanger tubes are installed in the heat exchanger. In reality, it forms a protective film. Therefore, when the corrosive environment is severe, sufficient anticorrosion effect is not obtained.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a heat exchanger tube for a U-shaped heat exchanger that can avoid corrosion even when used in a region with a severe corrosive environment, and a method for manufacturing the same.

[Means for Solving the Problem] The U-shaped heat exchanger tube for a heat exchanger according to the present invention is a heat exchanger tube for a heat exchanger made of copper or copper alloy and having a U-shaped curved shape.
It is characterized by having a protective film (an organic resin film or a film mainly composed of an inorganic material) with a thickness of 1 to 100 μm formed on the inner surface of the tube excluding a region of 50 mm or more from both ends of the tube.

Further, the method for manufacturing a U-shaped heat exchanger tube for a heat exchanger according to the present invention includes a step of providing a coating on predetermined portions of both ends of a U-shaped copper or copper alloy tube consisting of a straight tube portion and a curved tube portion. A spray nozzle is arranged at the boundary between the straight pipe section and the curved pipe section inside the pipe, and an organic resin paint or iron powder suspension is applied from the spray nozzle toward the inner surface of the curved pipe section. and a step of spouting the organic resin paint or iron powder suspension toward the inner surface of the straight pipe portion while moving the spray nozzle toward the end of the pipe.

In addition, when using an iron powder suspension, a step of feeding humid air into the pipe from the end of the pipe is provided after the iron powder suspension is ejected onto the inner surface of the straight pipe portion.

[Operation] In the U-shaped heat exchanger tube according to the present invention, no protective film is formed in the portions 50 mm or more from both tube ends. In heat transfer tubes, cathodic protection is usually performed from the ice chamber side to which cooling water is supplied, so that the ends of the tubes are sufficiently protected from corrosion by this cathodic protection. For this reason,
The inner surface of the tube end does not require a protective coating. In addition, when incorporating heat exchanger tubes into a heat exchanger, both ends of the heat exchanger tubes are expanded and pressed against the holes in the tube sheet and fixed to the tube sheet, so a protective film is formed on the tube ends. Even if it is
This protective film is removed during tube expansion. Also,
Since the coating substance adheres to the tube expansion tool, it is necessary to remove the attached coating substance, which is troublesome. Therefore, not only is it not necessary to form a protective film in advance in an area of 50 mm or more from the end of the tube, but it is also advantageous during use if no protective film is formed.

The thickness of the protective film is 1 to 100 μm. When the thickness of the protective film is 1 μm or less, the anticorrosion effect of the film is not sufficient. On the other hand, if the thickness of the protective film exceeds 100 μm,
Thermal conductivity as a heat transfer tube decreases. Therefore, the thickness of the protective film is set to 1 to 100 μm.

The protective film may be an organic resin such as an epoxy or alkyd resin, or an inorganic film containing iron hydroxide as a main component.

Next, in the method of the present invention, first, a coating is provided on the inner surface of both ends of the copper or copper alloy pipe, which is curved in a U-shape and consists of a straight pipe part and a bent pipe part, and then This also prevents the formation of a film on the end of the tube. and,
A spray nozzle is disposed at the boundary between the straight pipe section and the curved pipe section, and the organic resin paint or the iron powder suspension is jetted from the spray nozzle toward the inner surface of the curved pipe section.

Thereby, the organic resin paint or the iron powder suspension can be applied to the inner surface of the curved pipe portion of the pipe.

Thereafter, this spray nozzle is moved toward the end of the pipe, and during this movement, organic resin paint or iron powder suspension is sprayed onto the inner surface of the straight pipe portion.

Next, in the case of an organic resin paint, an organic protective film is obtained by drying the organic resin paint. In the case of an iron powder suspension, the iron powder is oxidized by supplying humid air into the pipe, and an inorganic film containing iron hydroxide or iron oxide as a main component is obtained. In this way,
A U-shaped heat exchanger tube for a heat exchanger having the above-mentioned protective film can be easily manufactured.

[Example] Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic vertical cross-sectional view showing a U-shaped heat exchanger tube according to the present embodiment, FIG. 2 is an enlarged vertical cross-sectional view thereof, and FIG. 3 is a cross-sectional view thereof.

The U-shaped heat exchanger tube for a heat exchanger according to this embodiment has an organic resin or an inorganic material containing iron hydroxide as a main component in the film-forming portion 2 on the inner surface of the heat exchanger tube element tube 3 that is bent into a U-shape. A protective film 4 consisting of the following is formed.

Both end portions of the raw pipe 3 are coat-free portions 1 .

The length of the film-free portion 1 in the tube axis direction is 50 mm or more, and in the film-free portion 1, the heat exchanger tube blank 3 made of copper or copper alloy is exposed. Also, what is the thickness of the protective film 4 formed on the film forming part 2? The range is from iooμm to iooμm.

As described above, the heat exchanger tube according to this embodiment has a high anticorrosion effect because the protective film is formed on the inner surface of the U-shaped tube. Further, since the coating 4 is not formed in the region extending 50 mm or more from the tube end, adhesion of the coating material to the tube expansion tool is prevented during tube expansion when the heat exchanger tube is assembled into a heat exchanger.

Next, the results of manufacturing the above-mentioned U-shaped heat exchanger tube for a heat exchanger by the method of this embodiment will be explained.

Aluminum brass tube with an outer diameter of 19.0 mm and a wall thickness of I, 1115 mm (JIS H3300CG372T)
was bent into a U-shape with a bending radius of 50 mm, 1100 mm, or 200 mm. The straight pipe portion of this U-shaped bent pipe is 2000 mm. And on the inner surface of these tubes,
An epoxy anti-corrosion paint was applied by the method shown below.

That is, first, 20.50 or 601 from both ends of the inner surface of the tube.
A removable cover has been installed over the area. Then, a spray nozzle for airless spray painting was inserted from the end of the tube, and this spray nozzle was placed at the boundary between the straight pipe part and the bent pipe part of the bent pipe.

Thereafter, nitrogen gas was supplied from around the spray nozzle to sufficiently replace the tube with nitrogen gas so that no air (oxygen) remained inside the tube.

Next, while supplying nitrogen gas from around the spray nozzle,
Spray coating was performed to paint the inner surface of the curved pipe section.

Next, after the painting of the curved pipe part is completed, the spray nozzle is moved toward the end of the pipe while spraying is applied.
The inner surface of the straight pipe part was painted. After the painting of this straight pipe portion was completed, the covers from both ends of the pipe were removed. In this way, Example 1 having a film having a film thickness shown in Table 1 below
Test tubes of Comparative Examples 1 to 3 and Comparative Examples 1 to 3 were obtained.

In addition, when painting by the air spray method, even if nitrogen was used instead of air as the gas for spraying the paint, the curved pipe portion could be painted in the same way.

In addition, a heat exchanger tube having an inorganic film containing iron hydroxide as a main component was manufactured by the method described below.

That is, first, a portion up to IO or 50 mm from both ends of the bent tube that had been subjected to the above-mentioned bending process was covered.

Then, an iron powder suspension was applied to the inner surface of the tube. In this case,
The iron powder suspension was applied to the inner surface of the tube in the same manner as in the case of the epoxy anticorrosive paint described above.

Next, moist air was blown from one end of the tube to oxidize the iron to form a protective film of an inorganic material containing iron hydroxide as the main component. In this way, test tubes of Examples 4 to 6 and Comparative Example 4 having coatings having the thickness shown in the coating thickness column of Table 1 were obtained.

In addition, as Comparative Examples 5 and 6, the bending radius of the curved pipe portion was 100 or 200 mm, respectively, and U without a protective film was used.
We also prepared a shape-shaped bent pipe.

Each test tube of these examples and comparative examples was attached to a model condenser, and a 6-month water flow test was conducted to examine its performance.

In this water flow test, 0, l of S2- was added to the natural seawater of the Kanmon Strait.
Added at a concentration of ppm for 2 hours every day, it was added to the tube at 2 m/min.
This was done by passing water at a flow rate of seconds.

In addition, after attaching the tube end of each test tube to a tube plate made of Nepalese brass by tube expansion processing, electricity was applied while maintaining the tube plate surface potential at -550 mV SCE using a constant potential electrolyzer, and the test tube was given cathodic protection. While doing so, the water was running.

After water flow was completed, the test tube was cut in half, and the depth of corrosion on the inner surface of each test tube was measured at several points. The maximum values of the corrosion depth are also shown in Table 1.

Further, a straight test tube having a length of 1000 mm was cut from the straight pipe portion of each test tube. Then, the outside of this straight test tube was made into a steam atmosphere at 100° C., room temperature industrial water was passed through the tube at a rate of 2 m/sec, and the overall heat transfer coefficient under steam condensation conditions was measured. In addition, the overall heat transfer coefficient of a new pipe without a protective film on the inner surface was measured under the same conditions, and the inner heat transfer resistance of the test tube was determined using the following equation 1.

L/K = 1/K o + γ - (1) However, K: Measured overall heat transfer coefficient of the test tube Ko: Measured overall heat transfer coefficient of the new pipe γ: Internal heat transfer resistance of the test tube It is shown in Table 1.

Furthermore, the tube expansion workability was evaluated based on whether or not membrane fragments adhered to the tube expansion tool when each test tube was attached to the tube sheet, and whether or not it took time and effort to clean it. The results are also shown in Table 1. However, in the table, cases where there was no trouble during pipe expansion work are indicated by ○, and cases where a film was attached to the tool and cleaning was time consuming are indicated by ×.

As is clear from Table 1, even in such a severe corrosive environment that Comparative Examples 5 and 6, which did not have a protective film, suffered corrosion of 0.22 mm or more, Examples 1 to 6 according to the present invention were all subject to maximum corrosion. The depth was less than 0.01 mm, indicating extremely little corrosion. Further, in Examples 1 to 6, the heat transfer resistance was 8. The QX to 'J' Ch/kca was small, less than 1, and no film was attached to the tool during pipe expansion work.

On the other hand, in Comparative Example 1, where the protective film is thin at 0.5 μm, the maximum corrosion depth is as deep as 0.18 mm, and in Comparative Example 2, where the protective film is thick at 120 μm, the heat transfer resistance is GX 10- '♂'Ch/kcal was extremely large. In addition, in Comparative Examples 3 and 4 in which the length of the non-film-formed portion from the tube end was shortened, the film adhered to the tool used for pipe expansion work, making cleaning of the tool complicated.

In addition, as mentioned above, in Comparative Examples 5 and 6 in which no film was present, the inner surface of the tube was similarly corroded.

[Effects of the Invention] As explained above, according to the present invention, an organic resin film or an inorganic film is applied to the inner surface of the U-shaped heat exchanger tube excluding an area of 50 mm or more from both ends of the tube. Since the film is formed with a predetermined thickness, corrosion of the heat transfer tube is prevented even under severe corrosive conditions, and heat transfer efficiency is high. Further, when the heat exchanger tube is assembled into the heat exchanger, a film will not be attached to the tube expansion tool.

Therefore, the U-shaped heat exchanger tube according to the present invention is extremely useful as a heat exchanger tube used under severe conditions.

Further, according to the method of the present invention, after providing a coating on the end of a copper or copper alloy pipe having a U-shaped curve, a spray nozzle is installed at the boundary between a straight pipe portion and a curved pipe portion of the pipe. After spraying organic resin paint or iron powder suspension to coat the inner surface of the curved pipe part, move the spray nozzle to the end of the pipe and spray directly. Since the pipe part is coated with an organic resin paint or iron powder suspension to form a protective film on the inner surface of the pipe except for a predetermined part of the pipe end, the U-shape has the above-mentioned excellent characteristics. The present invention has extremely excellent effects in preventing corrosion of U-shaped heat exchanger tubes, such as enabling industrial production of heat exchanger tubes for heat exchangers.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing a U-shaped heat exchanger tube according to an embodiment of the present invention, FIG. 2 is an enlarged vertical cross-sectional view thereof, and FIG. 3 is a cross-sectional view thereof. 1; Film-free portion, 2; Film-formed portion, 3; Heat exchanger tube element,
4; Protective film

Claims (4)

[Claims] (1) In a U-shaped curved copper or copper alloy heat exchanger tube, an organic film with a thickness of 1 to 100 μm is formed on the inner surface of the tube excluding an area of 50 mm or more from both tube ends. A heat exchanger tube for a U-shaped heat exchanger, characterized by having a resin film. (2) In a U-shaped curved copper or copper alloy heat exchanger tube, an inorganic substance with a film thickness of 1 to 100 μm is formed on the inner surface of the tube excluding an area of 50 mm or more from both ends of the tube. A heat exchanger tube for a U-shaped heat exchanger, characterized by having a film containing as a main component. (3) A step of providing a coating on predetermined portions of both ends of a U-shaped copper or copper alloy pipe consisting of a straight pipe portion and a bent pipe portion, and the straight pipe portion and the bent pipe portion inside the pipe. a step of arranging a spray nozzle at the boundary between the tube and spouting an organic resin paint from the spray nozzle toward the inner surface of the blood vessel portion, and moving the spray nozzle toward the end of the tube while spraying the inner surface of the straight tube portion. A method for manufacturing a heat exchanger tube for a U-shaped heat exchanger, comprising the step of spouting the organic resin paint toward the U-shaped heat exchanger. (4) A step of providing a coating on predetermined portions of both ends of a U-shaped copper or copper alloy pipe consisting of a straight pipe part and a bent pipe part, and the straight pipe part and the bent pipe part inside the pipe. a step of disposing a spray nozzle at the boundary between the curved pipe section and spouting an iron powder suspension from the spray nozzle toward the inner surface of the curved pipe section, and moving the spray nozzle toward the end of the pipe while Manufacturing a heat exchanger tube for a U-shaped heat exchanger, characterized by comprising a step of ejecting the iron powder suspension toward a partial inner surface, and a step of feeding moist air into the tube from an end of the tube. Method.